1/*
2 * Copyright © 2014 Intel Corporation
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining a
5 * copy of this software and associated documentation files (the "Software"),
6 * to deal in the Software without restriction, including without limitation
7 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8 * and/or sell copies of the Software, and to permit persons to whom the
9 * Software is furnished to do so, subject to the following conditions:
10 *
11 * The above copyright notice and this permission notice (including the next
12 * paragraph) shall be included in all copies or substantial portions of the
13 * Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
21 * IN THE SOFTWARE.
22 *
23 * Authors:
24 *    Jason Ekstrand (jason@jlekstrand.net)
25 *
26 */
27
28#include "nir.h"
29
30/*
31 * Implements "copy splitting" which is similar to structure splitting only
32 * it works on copy operations rather than the datatypes themselves.  The
33 * GLSL language allows you to copy one variable to another an entire
34 * structure (which may contain arrays or other structures) at a time.
35 * Normally, in a language such as C this would be handled by a "structure
36 * splitting" pass that breaks up the structures.  Unfortunately for us,
37 * structures used in inputs or outputs can't be split.  Therefore,
38 * regardlesss of what we do, we have to be able to copy to/from
39 * structures.
40 *
41 * The primary purpose of structure splitting is to allow you to better
42 * optimize variable access and lower things to registers where you can.
43 * The primary issue here is that, if you lower the copy to a bunch of
44 * loads and stores, you loose a lot of information about the copy
45 * operation that you would like to keep around.  To solve this problem, we
46 * have a "copy splitting" pass that, instead of splitting the structures
47 * or lowering the copy into loads and storres, splits the copy operation
48 * into a bunch of copy operations one for each leaf of the structure tree.
49 * If an intermediate array is encountered, it is referenced with a
50 * wildcard reference to indicate that the entire array is to be copied.
51 *
52 * As things become direct, array copies may be able to be losslessly
53 * lowered to having fewer and fewer wildcards.  However, until that
54 * happens we want to keep the information about the arrays intact.
55 *
56 * Prior to the copy splitting pass, there are no wildcard references but
57 * there may be incomplete references where the tail of the deref chain is
58 * an array or a structure and not a specific element.  After the copy
59 * splitting pass has completed, every variable deref will be a full-length
60 * dereference pointing to a single leaf in the structure type tree with
61 * possibly a few wildcard array dereferences.
62 */
63
64struct split_var_copies_state {
65   nir_shader *shader;
66   void *dead_ctx;
67   bool progress;
68};
69
70/* Recursively constructs deref chains to split a copy instruction into
71 * multiple (if needed) copy instructions with full-length deref chains.
72 * External callers of this function should pass the tail and head of the
73 * deref chains found as the source and destination of the copy instruction
74 * into this function.
75 *
76 * \param  old_copy  The copy instruction we are splitting
77 * \param  dest_head The head of the destination deref chain we are building
78 * \param  src_head  The head of the source deref chain we are building
79 * \param  dest_tail The tail of the destination deref chain we are building
80 * \param  src_tail  The tail of the source deref chain we are building
81 * \param  state     The current split_var_copies_state object
82 */
83static void
84split_var_copy_instr(nir_intrinsic_instr *old_copy,
85                     nir_deref_var *dest_head, nir_deref_var *src_head,
86                     nir_deref *dest_tail, nir_deref *src_tail,
87                     struct split_var_copies_state *state)
88{
89   assert(src_tail->type == dest_tail->type);
90
91   /* Make sure these really are the tails of the deref chains */
92   assert(dest_tail->child == NULL);
93   assert(src_tail->child == NULL);
94
95   switch (glsl_get_base_type(src_tail->type)) {
96   case GLSL_TYPE_ARRAY: {
97      /* Make a wildcard dereference */
98      nir_deref_array *deref = nir_deref_array_create(state->dead_ctx);
99      deref->deref.type = glsl_get_array_element(src_tail->type);
100      deref->deref_array_type = nir_deref_array_type_wildcard;
101
102      /* Set the tail of both as the newly created wildcard deref.  It is
103       * safe to use the same wildcard in both places because a) we will be
104       * copying it before we put it in an actual instruction and b)
105       * everything that will potentially add another link in the deref
106       * chain will also add the same thing to both chains.
107       */
108      src_tail->child = &deref->deref;
109      dest_tail->child = &deref->deref;
110
111      split_var_copy_instr(old_copy, dest_head, src_head,
112                           dest_tail->child, src_tail->child, state);
113
114      /* Set it back to the way we found it */
115      src_tail->child = NULL;
116      dest_tail->child = NULL;
117      break;
118   }
119
120   case GLSL_TYPE_STRUCT:
121      /* This is the only part that actually does any interesting
122       * splitting.  For array types, we just use wildcards and resolve
123       * them later.  For structure types, we need to emit one copy
124       * instruction for every structure element.  Because we may have
125       * structs inside structs, we just recurse and let the next level
126       * take care of any additional structures.
127       */
128      for (unsigned i = 0; i < glsl_get_length(src_tail->type); i++) {
129         nir_deref_struct *deref = nir_deref_struct_create(state->dead_ctx, i);
130         deref->deref.type = glsl_get_struct_field(src_tail->type, i);
131
132         /* Set the tail of both as the newly created structure deref.  It
133          * is safe to use the same wildcard in both places because a) we
134          * will be copying it before we put it in an actual instruction
135          * and b) everything that will potentially add another link in the
136          * deref chain will also add the same thing to both chains.
137          */
138         src_tail->child = &deref->deref;
139         dest_tail->child = &deref->deref;
140
141         split_var_copy_instr(old_copy, dest_head, src_head,
142                              dest_tail->child, src_tail->child, state);
143      }
144      /* Set it back to the way we found it */
145      src_tail->child = NULL;
146      dest_tail->child = NULL;
147      break;
148
149   case GLSL_TYPE_UINT:
150   case GLSL_TYPE_INT:
151   case GLSL_TYPE_FLOAT:
152   case GLSL_TYPE_DOUBLE:
153   case GLSL_TYPE_BOOL:
154      if (glsl_type_is_matrix(src_tail->type)) {
155         nir_deref_array *deref = nir_deref_array_create(state->dead_ctx);
156         deref->deref.type = glsl_get_column_type(src_tail->type);
157         deref->deref_array_type = nir_deref_array_type_wildcard;
158
159         /* Set the tail of both as the newly created wildcard deref.  It
160          * is safe to use the same wildcard in both places because a) we
161          * will be copying it before we put it in an actual instruction
162          * and b) everything that will potentially add another link in the
163          * deref chain will also add the same thing to both chains.
164          */
165         src_tail->child = &deref->deref;
166         dest_tail->child = &deref->deref;
167
168         split_var_copy_instr(old_copy, dest_head, src_head,
169                              dest_tail->child, src_tail->child, state);
170
171         /* Set it back to the way we found it */
172         src_tail->child = NULL;
173         dest_tail->child = NULL;
174      } else {
175         /* At this point, we have fully built our deref chains and can
176          * actually add the new copy instruction.
177          */
178         nir_intrinsic_instr *new_copy =
179            nir_intrinsic_instr_create(state->shader, nir_intrinsic_copy_var);
180
181         /* We need to make copies because a) this deref chain actually
182          * belongs to the copy instruction and b) the deref chains may
183          * have some of the same links due to the way we constructed them
184          */
185         new_copy->variables[0] = nir_deref_var_clone(dest_head, new_copy);
186         new_copy->variables[1] = nir_deref_var_clone(src_head, new_copy);
187
188         /* Emit the copy instruction after the old instruction.  We'll
189          * remove the old one later.
190          */
191         nir_instr_insert_after(&old_copy->instr, &new_copy->instr);
192         state->progress = true;
193      }
194      break;
195
196   case GLSL_TYPE_SAMPLER:
197   case GLSL_TYPE_IMAGE:
198   case GLSL_TYPE_ATOMIC_UINT:
199   case GLSL_TYPE_INTERFACE:
200   default:
201      unreachable("Cannot copy these types");
202   }
203}
204
205static bool
206split_var_copies_block(nir_block *block, struct split_var_copies_state *state)
207{
208   nir_foreach_instr_safe(instr, block) {
209      if (instr->type != nir_instr_type_intrinsic)
210         continue;
211
212      nir_intrinsic_instr *intrinsic = nir_instr_as_intrinsic(instr);
213      if (intrinsic->intrinsic != nir_intrinsic_copy_var)
214         continue;
215
216      nir_deref_var *dest_head = intrinsic->variables[0];
217      nir_deref_var *src_head = intrinsic->variables[1];
218      nir_deref *dest_tail = nir_deref_tail(&dest_head->deref);
219      nir_deref *src_tail = nir_deref_tail(&src_head->deref);
220
221      switch (glsl_get_base_type(src_tail->type)) {
222      case GLSL_TYPE_ARRAY:
223      case GLSL_TYPE_STRUCT:
224         split_var_copy_instr(intrinsic, dest_head, src_head,
225                              dest_tail, src_tail, state);
226         nir_instr_remove(&intrinsic->instr);
227         ralloc_steal(state->dead_ctx, instr);
228         break;
229      case GLSL_TYPE_FLOAT:
230      case GLSL_TYPE_DOUBLE:
231         if (glsl_type_is_matrix(src_tail->type)) {
232            split_var_copy_instr(intrinsic, dest_head, src_head,
233                                 dest_tail, src_tail, state);
234            nir_instr_remove(&intrinsic->instr);
235            ralloc_steal(state->dead_ctx, instr);
236         }
237         break;
238      case GLSL_TYPE_INT:
239      case GLSL_TYPE_UINT:
240      case GLSL_TYPE_BOOL:
241         assert(!glsl_type_is_matrix(src_tail->type));
242         break;
243      default:
244         unreachable("Invalid type");
245         break;
246      }
247   }
248
249   return true;
250}
251
252static bool
253split_var_copies_impl(nir_function_impl *impl)
254{
255   struct split_var_copies_state state;
256
257   state.shader = impl->function->shader;
258   state.dead_ctx = ralloc_context(NULL);
259   state.progress = false;
260
261   nir_foreach_block(block, impl) {
262      split_var_copies_block(block, &state);
263   }
264
265   ralloc_free(state.dead_ctx);
266
267   if (state.progress) {
268      nir_metadata_preserve(impl, nir_metadata_block_index |
269                                  nir_metadata_dominance);
270   }
271
272   return state.progress;
273}
274
275bool
276nir_split_var_copies(nir_shader *shader)
277{
278   bool progress = false;
279
280   nir_foreach_function(function, shader) {
281      if (function->impl)
282         progress = split_var_copies_impl(function->impl) || progress;
283   }
284
285   return progress;
286}
287